1. Field of the Invention
The present invention relates to a liquid discharge head substrate for recording by discharging liquid and a liquid discharge head equipped with the liquid discharge head substrate and specifically to a liquid discharge head substrate and liquid discharge head for discharging ink (hereinafter also referred to as recording head).
2. Description of the Related Art
An inkjet recording apparatus performs a recording operation such that ink is film-boiled by the use of thermal energy generated by heating elements arranged on a liquid discharge head substrate of a recording head and ink is discharged onto a recording medium by the use of the foaming pressure generated by the film boiling. In such a liquid discharge head substrate, a protecting layer is provided over the heating elements to prevent the heating elements from not only being corroded by ink, but also being destroyed by cavitation generated at the time of defoaming. However, the protecting layer provided over the heating elements prevents the heat of the heating elements from efficiently reaching the ink, which consumes extra electric power to bubble the ink.
In this regard, U.S. Pat. No. 6,042,221 discusses a method for improving thermal efficiency by partially thinning the protecting layer over the heating elements to achieve power saving. In a recording head discussed in U.S. Pat. No. 6,042,221, a thin protecting layer is provided in an area which becomes high in temperature at the time of operating heating elements and a thick protecting layer is provided in an area which becomes low in temperature at the time of operating heating elements to efficiently transmit heat to ink, thereby saving power.
In recent years, there has been a demand for discharging ink at a high frequency to perform a recording operation at a high speed and increasing the number of heating elements to increase a width of recording per scanning, which has increased a length in the direction of column of heating elements on a liquid discharge head substrate. On the other hand, there has been a demand to acquire a large number of substrates for a liquid discharge head from a single wafer by reducing the area of a liquid discharge head substrate to lower a manufacturing cost for a liquid discharge head substrate. As a result, it is necessary to reduce the width in the direction orthogonal to the column direction in which heating elements are arranged. Discharging ink at a high frequency by using such a liquid discharge head substrate may cause an uneven temperature distribution on the liquid discharge head substrate because the center portion of the liquid discharge head substrate is more liable to accumulate heat than the end portion thereof.
Therefore, even if the recording head discussed in U.S. Pat. No. 6,042,221 is used, the size of a bubble is varied depending on the temperature of the substrate to cause the dispersion of discharge of ink, which may affect the quality of a recorded image.